Torque motor driven spool valves are well known in the art including such valves which operate through the utilization of a rotary torque motor having a drive member extending from the rotor thereof into contact with the spool valve to directly reciprocate the spool valve within a bore provided in the valve housing. When the spool valve reciprocates it controls the flow of fluid from a source thereof to a load in response to the electrical signals applied to the drive motor.
Direct drive servo valves of the type above mentioned are illustrated in the following U.S. Pat. Nos. 2,697,016, 2,769,943, 4,339,737, 4,197,474, 4,452,423, 4,793,337, 5,052,441 and 5,040,568.
In all such direct drive servo valves known to Applicant, the spool valve is reciprocated by the free end of the motor shaft contacting the spool through an eccentrically mounted pin having a substantially spherical drive tip. The drive tip is inserted into a well or annular groove formed in the spool. The dimensional relationship between the spherical drive tip and the spool is such as to provide minimal frictional forces and near zero backlash. Utilizing such dimensions necessitates lapping and fitting operations which add greatly to the expense of such devices.